function clickedImage(event, id) {
    var x = event.offsetX ? (event.offsetX) : event.layerX - document.getElementById(id).offsetLeft;
    var y = event.offsetY ? (event.offsetY) : event.layerY - document.getElementById(id).offsetTop;
    document.mainForm.x.value = x;
    document.mainForm.y.value = y;
    document.mainForm.submit();
}